Star-block copolymers PEI-g-PZLL with a branched polyethylenimine (PEI) core and multiple grafted poly(ε-benzyloxycarbonyl-L-lysine) (PZLL) peripheral chains were designed, synthesized, and evaluated as nanocarriers for indomethacin (IND). In an aqueous solution, PEI-g-PZLL self-assembled into spherical nanoparticles capable of encapsulating IND at high loading capacity and loading efficiency. Differential scanning calorimetry and X-ray diffraction measurements indicated that IND was molecularly or amorphously dispersed in the nanoparticles. Fourier transform infrared spectra revealed the presence of multiple intermolecular interactions, including hydrogen bonding, electrostatic forces, π–π stacking and hydrophobic interactions, between the block copolymer and the IND molecules. IND-loaded nanoparticles exhibited fast release under intestinal pH. Compared with raw IND, the utilization of PEI-g-PZLL as a carrier significantly enhanced the oral bioavailability of IND and improved its protective effect on renal ischemia-reperfusion injury, as evidenced by in vivo pharmacokinetic and pharmacodynamic studies. Cytotoxicity assay, histological observation and cellular uptake study suggested that PEI-g-PZLL was fairly biocompatible. All these results indicated that star-block copolymers PEI-g-PZLL could be used as efficient nanocarriers for IND and other poorly water-soluble drugs.Statement of SignificanceThe use of polyethylenimine (PEI) as an oral drug delivery carrier is limited because it is not biodegradable and the use of higher molecular weight PEI leads to improved efficiency but also increased cytotoxicity. The design of functionalized PEIs with low cytotoxicity and high efficiency is crucial for developing a successful oral drug delivery system. In our study, poly(ε-benzyloxycarbonyl-L-lysine) (PZLL)-grafted branched PEI (PEI-g-PZLL) was reported as an oral nanocarrier for indomethacin (IND). The low cytotoxicity and biodegradability, well-defined self-assembled nano-sized polymeric micelles, high loading capacity and loading efficiency, amorphous state of the encapsulated IND, as well as the enhanced oral bioavailability of IND, makes the copolymer PEI-g-PZLL a promising nanocarrier for the oral administration of IND and possibly other poorly water-soluble drugs.Download high-res image (192KB)Download full-size image

The purpose of this research was to evaluate the protective effects of insulin-loaded poly(ethylene glycol)-b-poly((2-aminoethyl-l-glutamate)-g-poly(l-lysine)) (PEG-b-P(ELG-g-PLL)) on renal ischemia/reperfusion (I/R) injury in rats with diabetes mellitus. Rats were preconditioned with free insulin or insulin/PEG-b-P(ELG-g-PLL) polyplexes, then subjected to renal I/R. The blood and kidneys were then harvested, Glucose uptake rate, glucose transporter 4 (GULT4) mRNA level, cell membrane GULT4 content and GULT4 expression were measured, the level of serum creatinine and blood urea nitrogen were determined, the activity of superoxide dismutase and inducible nitric oxide synthase, the content of malondialdehyde and nitric oxide, reactive oxygen species (ROS) production and nuclear factor κB (NF-κB) mRNA level, Bcl-2 assaciated x protein (Bax) mRNA and B cell lymphoma/lewkmia-2 (Bcl-2) mRNA level, and the expression of protein 47 kDa phagocyte oxidase (p47phox) in renal tissues were measured. Insulin preconditioning improved the recovery of renal function, reduced oxidative stress injury, restored nitroso-redox balance and downregulated the expression of p47phox induced by renal I/R injury, while the application of block copolymer PEG-b-P(ELG-g-PLL) as an insulin nanocarrier significantly enhanced the protective effect of insulin. Block copolymer PEG-b-P(ELG-g-PLL) could be used as a potential nanocarrier for insulin with sustained release and enhanced bioavailability.Download high-res image (79KB)Download full-size image

Cylindrical copolypeptide brush PLLF-g-(PLF-b-PLL), consisting of a poly(L-lysine-co-L-phenylalanine) (PLLF) backbone and poly(L-phenylalanine)-b-poly(L-lysine) (PLF-b-PLL) amphiphilic block copolypeptide side chains, has been synthesized, characterized, and evaluated as drug and gene carriers. PLLF-g-(PLF-b-PLL) brushes were synthesized by the multi-step ring-opening polymerization of amino acid N-carboxyanhydrides via a “grafting from” strategy. Transmission electron microscopy measurements and pyrene probe fluorescence study revealed that the synthesized copolypeptide brushes adopted nanosized cylindrical morphologies which resembled unimolecular polymeric micelles with a hydrophobic PLF core and a hydrophilic PLL periphery. An encapsulation study demonstrated that hydrophobic molecules (e.g., pyrene and oil red O) can be solubilized in the core of the copolypeptide brushes, while anionic hydrophilic molecules (e.g., rose bengal and methyl orange) can be entrapped into the brush periphery. Hydrophobic molecules and hydrophilic guests can be encapsulated simultaneously in a site-isolated state. Furthermore, the in vitro gene transfection efficiencies of copolypeptide brushes were evaluated in HEK293 and HeLa cells. The synthesized copolypeptide brushes exhibited low cytotoxicity and mediated efficient gene transfection. Our research suggested that these cylindrical copolypeptide brushes with a brush-like PLL periphery could be used as promising carriers for the codelivery of drugs and genes.

The self-assembly of amphiphilic peptide I3K (Ac-I3K-NH2) and its potential application as a drug nanocarrier have been investigated. I3K monomers and nanotubular segments were initially the dominant species in aqueous solution and they gradually self-assembled into mature nanotubes with heights of approximately 12 nm and lengths of more than 1 μm. The encapsulation properties of the self-assembled peptide nanotubes were then investigated using model compound guests, including anionic hydrophilic methyl orange (MO) and hydrophobic oil red. It revealed that the model compounds could be efficiently encapsulated by I3K assemblies via electrostatic and hydrophobic interactions, respectively. Atomic force microscopy images demonstrated that variations in drug concentration did not significantly alter the structures of the peptide assemblies but could affect their sizes. Circular dichroism analyses indicated the predominance of β-sheet conformation associated with the self-assembled system regardless of drug concentrations. The in vitro releasing behavior of the encapsulated model drugs was also studied by the techniques of dialysis. The entrapped model drug MO exhibited an accelerated release as the solution pH was either decreased to 2.0–3.0 or increased to 10.0–11.0 but revealed a sustained release at physiological pH. These results demonstrated that these self-assembled peptide nanotubes could serve as potential drug nanocarriers with efficient encapsulation ability, and sustained and pH-responsive release properties.

A novel star-shaped copolymer PEI10 000-g-PLL20, with a hyperbranched polyethylenimine (PEI) core and multiple linear poly(L-lysine) (PLL) peripheral chains was designed and synthesized. The star-shaped peptide, along with multiple counterions, was used as an organic template to direct the biomimetic synthesis of silica under mild conditions. Various biosilica morphologies, such as spherical, clubbed, and hexagonal shapes, were transformed using a specific TEOS/lysine residue ratio (δ) in a peptide/phosphate/silicic acid system. Individual silica spheres were obtained when δ was smaller than 10, whereas clubbed (δ = 11) and hexagonal (δ = 18) particles formed when δ was larger than 10. However, only clubbed biosilica was obtained when the counterions were carbonates or sulfates. Transmission electron microscopy and circular dichroism spectroscopy results suggest that the presence of counterions was necessary but not sufficient to produce ordered silica morphologies. Thus, the nature of peptide/anion complex, TEOS/lysine residue ratio, and pH changes in the biomimetic system played important roles in determining the silica morphologies.

Star-block copolymers PEI-g-(PLG-b-PEG), which consist of a hyperbranched polyethylenimine (PEI) core, a poly(l-glutamic acid) (PLG) inner shell, and a poly(ethylene glycol) (PEG) outer shell, were synthesised and evaluated as nanocarriers for cationic drugs. The synthesised star-block copolymers were characterised by 1H NMR, gel permeation chromatography (GPC), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Crystal violet (CV), as a model cationic dye, and doxorubicin hydrochloride (DOX), as a model anticancer drug, could be efficiently entrapped by the synthesised star-block copolymers at physiological pH as a result of electrostatic interactions between the cationic guest molecules and the negatively charged PLG segments in the PEI-g-(PLG-b-PEG) host. The drug–polymer complexes showed relatively high temporal stability at physiological pH and sustained release of the encapsulated drugs was observed. The entrapped model compounds demonstrated accelerated release as the pH was gradually decreased.Graphical abstractHighlights► We design and synthesise poly(l-glutamic acid)-based star-block copolymers. ► Copolymers show efficient encapsulation towards cationic drugs. ► Polymer–drug complexes are stable at physiological pH. ► Encapsulated drugs demonstrate accelerated release at lower pH.

Star-block quadripolymers PEI-g-(PLF-b-PLL-b-PEG) and PEI-g-(PLF-b-PLG-b-PEG) [i.e., a polyethylenimine (PEI) core, an amphiphilic copolypeptide poly(l-phenylalanine)-b-poly(l-lysine) (PLF-b-PLL) or poly(l-phenylalanine)-b-poly(l-glutamic acid) (PLF-b-PLG) inner shell, and a poly(ethylene glycol) (PEG) outer shell] were synthesized, characterized, and evaluated as drug nanocarriers. The star-block quadripolymers were obtained by sequential ring-opening polymerizations of l-phenylalanine N-carboxyanhydride and ε-benzyloxycarbonyl-l-lysine N-carboxyanhydride or γ-benzyl-l-glutamate N-carboxyanhydride initiated by the terminal primary amines of PEI. Subsequently, the periphery was PEGylated, and the poly(l-lysine) or poly(l-glutamic acid) side chains were deprotected. The synthesized star-block quadripolymers were characterized with 1H NMR, gel permeation chromatography (GPC), and laser light dynamic scattering (DLS). These polymers were well dispersed in aqueous solutions and resembled amphiphilic unimolecular micelles. The encapsulation study demonstrated that these polymers can solubilize nonpolar model compounds through hydrophobic interactions. Dialysis and spectrophotometric titration experiments indicated that these polymers could efficiently encapsulate hydrophilic model compounds via electrostatic interactions. Furthermore, the synthesized quadripolymers could entrap hydrophobic and hydrophilic model compounds in the site-isolated state simultaneously. The entrapped hydrophilic model compounds demonstrated sustained release at physiological pH and accelerated release when the pH was either increased or decreased. The simultaneous encapsulation of versatile guest molecules as well as the pH-responsive releasing properties of these star-block quadripolymers could be potentially useful in the controlled drug co-delivery applications.Graphical abstract.Highlights► We design and synthesize two polypeptide-based star-block quadripolymers. ► Quadripolymers resemble amphiphilic unimolecular micelles. ► Quadripolymers solubilize hydrophobic molecules via hydrophobic interactions. ► Quadripolymers encapsulate hydrophilic drugs through electrostatic interactions. ► Quadripolymers entrap hydrophobic and hydrophilic guest molecules simultaneously in the site-isolated state.

Cylindrical copolypeptide brushes PLLF-g-(PLF-b-PLG) with poly(l-lysine-co-l-phenylalanine) (PLLF) as the backbone and poly(l-phenylalanine)-b-poly(l-glutamic acid) (PLF-b-PLG) as the side chains have been synthesized and evaluated as drug delivery carriers. The synthesized copolypeptide brushes were characterized by 1H NMR, gel permeation chromatography (GPC), and transmission electron microscopy (TEM). In aqueous solution, the copolypeptide brushes adopt cylindrical morphologies and resemble unimolecular polymeric micelles with a hydrophobic poly(l-phenylalanine) core and a hydrophilic poly(l-glutamate) shell. An encapsulation study demonstrated that these water soluble, biodegradable copolypeptide brushes encapsulate hydrophobic compounds and cationic hydrophilic guest molecules simultaneously. Furthermore, the encapsulated cationic model compounds exhibit a pH-responsive releasing property.Graphical abstractHighlights► We design and synthesize amphiphilic cylindrical copolypeptide brushes. ► Copolypeptide brushes resemble unimolecular micelles. ► Copolypeptide brushes encapsulate hydrophobic and cationic guest molecules simultaneously. ► Structure of these polymer brushes is easily extended and modulated.

Star-block copolymers PEI-g-(PLL-b-PEG) with a branched polyethylenimine (PEI) core, a poly(l-lysine) (PLL) inner shell, and a poly(ethylene glycol) (PEG) outer shell have been synthesised and evaluated as potential nanocarriers for anionic drugs. The star-block copolymers were synthesised by a ring-opening polymerisation of ɛ-benzyloxycarbonyl-l-lysine N-carboxyanhydride initiated by the peripheral primary amino groups of PEI, surface modification with activated PEG 4-nitrophenyl carbonate, and subsequent deprotection of benzyl groups on the side chains of the PLL inner shell. The synthesised star-block copolymers were characterised by 1H NMR, gel permeation chromatography (GPC), and dynamic light scattering (DLS). The encapsulation properties of these star-block copolymers were characterised by spectrophotometric titration and dialysis. These techniques demonstrated that anionic model dyes, such as methyl orange and rose Bengal, and the model drug diclofenac sodium can be encapsulated efficiently by PEI-g-(PLL-b-PEG) at physiological pH. The entrapped model compounds demonstrated sustained release at physiological pH and accelerated release when the pH was either increased to 10.0–11.0 or decreased to 2.0–3.0. The efficient encapsulation as well as the pH-responsive releasing properties of these star-block copolymers could be potentially used in the controlled release of anionic drugs.Graphical abstractHighlights► We design and synthesize poly(l-lysine)-based star-block copolymers. ► Copolymers show efficient encapsulation towards anionic drugs. ► Polymer–drug complexation is characterized by spectrophotometric titration. ► Polymer–drug complex is stable at physiological pH. ► Encapsulated drugs demonstrate accelerated release at higher or lower pH.